1. Field of the Invention
The present invention relates to a method for calibrating an infrared thermometer, particularly to a method for calibrating an infrared thermometer at different ambient temperatures.
2. Description of the Related Art
U.S. Pat. No. 6,065,866 discloses a method for calibrating an infrared thermometer. In this prior art, an infrared thermometer detects two black bodies 1 and 2, which respectively have given temperatures Ts(1) and Ts(2), at an identical ambient temperature TU, and then the radiation sensor of the infrared thermometer outputs signals U(1) and U(2). Thus, the sensitivity S of the radiation sensor can be obtained from Equation (1):
                                                                        T                s                            ⁡                              (                1                )                                      4                    =                                                    U                ⁡                                  (                  1                  )                                            S                        +                          T              U              4                                      ⁢                                  ⁢                                                            T                s                            ⁡                              (                2                )                                      4                    =                                                    U                ⁡                                  (                  2                  )                                            S                        +                          T              U              4                                                          (        1        )            and the value of the sensitivity S of the radiation sensor is
            U      ⁡              (        2        )              -          U      ⁡              (        1        )                                Ts        ⁡                  (          2          )                    4        -                  Ts        ⁡                  (          1          )                    4      Then, the values of the ambient temperature TU can be further obtained from Equation (1).
Infrared thermometers are very sensitive to ambient temperature. For example, when the measurement accuracy of an infrared ear thermometer is ±0.2° C., the variation of ambient temperature ΔTU should be limited to within ±0.2° C. or the accuracy of the infrared ear thermometer will be influenced. However, maintaining a constant ambient temperature is very difficult. For example, when the door is open and close for someone entering or leaving an air-conditioned room, the temperature will be influenced. Further, each person entering or leaving the room has his own body temperature. Therefore, limiting the variation of ambient temperature ΔTU to within ±0.2° C. is very difficult. Only by investing much money in related equipment can it be achieved.
Accordingly, the present invention proposes a new method for calibrating an infrared thermometer to overcome the above-mentioned problems.